1. Field of the Invention
The present invention relates to a method for preserving a liquid-ejection head that has a movable member to be displaced by an effect of generating a bubble by the action of thermal energy on a liquid, which can be applicable to a printer, a copy machine, a facsimile machine equipped with a communication system, a word processor equipped with a printer component, and so on, and further to an industrial printing apparatus to be provided as an integrated system in combination with various processing devices, for printing an image or the like on a printing medium such as paper, yarn, fiber, cloth, leather, metal, plastic, glass, wood, ceramic or the like. Furthermore, the present invention relates to a liquid-ejection apparatus with means responsible for performing the method described above and with a portion where the liquid-ejection head described above can be installed.
2. Description of the Related Art
Conventionally, so-called bubble-jet printing method has been known as an ink-jet printing method. The method comprises the steps of providing an ink with an energy such as a thermal energy to cause abrupt volume variation (generation of bubble) of the ink, and of ejecting the ink through ejection ports by an acting force on the basis of the state variation to deposit the ejected ink on a printing medium to form an image. In a printing apparatus using the bubble-jet printing method, ejection ports for ejecting the ink, ink passages communicating with the ejection ports, and electrothermal transducers as energy generating means for ejecting ink in the ink passages are typically arranged as disclosed in U.S. Pat. No. 4,723,129 and the like.
With such printing method, high quality image can be printed at high speed and low noise. A printing head implementing this method has many merits that high resolution image and color image can be easily obtained because the ejection ports for ejecting the ink can be arranged at high density. Recently, the bubble-jet printing method has been employed in a large number of office use apparatus, such as printers, copy machines, facsimile machines and the like, and is also applicable to industrial system, such as a textile printing apparatus.
According to spreading of application of the bubble-jet technology in various kinds of products, the following demands are recently growing: for example, optimization of a heater as energy generating means is studied in order to demand for improvement of an energy efficiency. As the optimization of the heater, adjustment of a thickness of a protective layer for standing between the heater and the ink can be nominated. This method is effective for improvement of a transmission efficiency to a generated head to the liquid such as the ink.
On the other hand, in order to obtain high quality image, there has been proposed a driving condition for providing the liquid ejecting method or the like enabling high speed ink ejection and ink injection in good condition based on stable bubble generation. Also, in viewpoint of high speed printing, there has been proposed a printing apparatus with an improved liquid-flowing passage configuration for obtaining the liquid-ejection head having high speed re-fill. Here, "re-fill" means liquid supply from the common liquid chamber to ejection ports through liquid-flowing passages when liquid is ejected from the ejection port to generate negative pressure near the ejection port in the liquid-flowing passage or when bubbles in the liquid shrinks after the pressure generated on growth of the bubbles are utilized for ejection of the liquid.
Among the liquid-flowing passage configuration, the flow passage structure as shown in FIGS. 1A and 1B has been disclosed in Japanese Patent Application Laid-Open No. 199972/1988. The disclosed liquid-flowing passage structure and the head fabrication method are inventions work out in view of a back wave generated associating with generating of the bubble. The back wave is generated by pressure directed toward opposite direction to a direction toward the ejection port, namely a pressure directed to a common liquid chamber 1005. The back wave does not act as an energy in the direction of ink-ejection, so that it is known as a loss energy that reduces an amount of energy for the ink-ejection.
A liquid-ejection head shown in FIGS. 1A and 1B comprises a plurality of heaters 1002 on a single substrate 1001. Each of the heater 1002 is provided as an element for generating an ejection energy for ejecting the liquid. On the substrate 1001, furthermore, a plurality of liquid-flowing passages 1003 are arranged in parallel so as to correspond to their respective heaters 1002. In addition, each of the liquid-flowing passage 1003 is communicated with an individual ejection port 1004, and also communicated with a common liquid chamber designed to supply a liquid into each of them in an amount corresponding to a liquid ejected from the ejection port 1004. As shown in the figures, furthermore, there is a valve 1007 located at a position away from a region, in which the bubble is generated by the heater 1002, and at opposite side to the ejection port 11 with respect to the heater 1002.
In this embodiment, the valve 1007 is prepared as in the form of a plate with one end thereof being fixed on an upper plate provided as a ceiling of the liquid-flowing passage 1003. If the valve 1007 is not subjected to an effect of the bubble generation, a surface of the valve is substantially being attached to a surface of the ceiling. If a bubble 1006 is generated and effects on the valve 1007, as shown in FIG. 1B, a free end of the valve 1007 moves in a curved path and hangs down into the liquid-flowing passage 1003. This invention is disclosed to restrict energy loss by controlling a part of the back wave (i.e., a pressure directed toward the liquid chamber 1005, indicated by the arrow A) by means of the valve 1007.
By the way, the liquid-ejection head shown in FIGS. 1A and 1B is in the type of a set of liquid-flowing passages (also referred as the nozzles) being arranged in parallel as a single-layered structure, in which the heaters 1002 are provided in the respective liquid-flowing passages 1003 communicated with their ejection ports 1004. In this type of the head, however, there is a problem of ejection failure to be caused by clogging the nozzle. When the nozzle is not in use for a long time, a liquid such as ink in the nozzle may be dried and solidified and then solid contents thereof may be attached to an inner wall of the nozzle to cause ejection failure. If the nozzle is clogged up with the solidified ink, it is difficult to remove the clogging material by performing a typical recovery process, such as preparatory ejection or suction recovery to refill a flesh ink into the nozzle.
Conventionally, therefore, the clogging material being firmly fixed to the nozzle's inner wall is forcefully removed by a typical recovery process in combination with an additional process comprised of, for example repeating the cycle of heating and drawing (i.e., the process of forcefully melting the solidified ink), washing with a detergent to remove the fixed material from the nozzle, forcefully destroying the fixed material by an ultrasonically vibration or an ultrasonic cleaning, or the like. However, all of these recovery processes are not appropriate because it is necessary for a man skilled in the art to apply one of the recovery processes after that the solidified ink is firmly attached to the nozzle's surface.
In the liquid-ejection head with the construction as set forth, as can be appreciated from the study for the behavior of a liquid upon the generation of a bubble 1006 in the liquid-flowing passage 1003 that retains the liquid to be ejected, it is not practical to restrict a part of the back wave by means of the valve 1007 for the liquid ejection.
In nature, the back wave per se is not directly associated with the ejection as set forth above. When the back wave is generated within the liquid-flowing passage 1003 as shown in FIG. 1A, a pressure directly associated with ejection of the liquid is already places the liquid from the liquid-flowing passage 1003 in condition permitting ejection thereof. Accordingly, even when a part of the back wave is restricted, no significant effect may be provided for ejection.
On the other hand, in the bubble-jet printing method, since the heater repeats heating in a condition contacting with the ink, a deposit due to baking of the ink is generated on the surface of the heater. In certain kind of the liquid or ink, large amount of deposit is generated to make generation of bubble unstable. Also, when the liquid to be ejected has a property to be easily degraded the quality by heat, or when the liquid is difficult to generate an appropriate bubble, it has been desired to provide a method to achieve good ejection without causing change of property of the liquid to be ejected.
In such viewpoint, a method to use a liquid (bubble-generation liquid) to generate bubble by a heat, which is different from a liquid (ejection liquid) to be ejected, to transmit a pressure generated by growing a bubble to the ejection liquid to perform ejection, has been disclosed in Japanese Patent Application Laid-Open No. 69467/1986, Japanese Patent Application Laid-Open No. 81172/1980, U.S. Pat. No. 4,480,259 and so on. In these publications, an ink as the ejection liquid and the bubble-generation liquid are completely separated by a flexible membrane formed of a silicon rubber or the like so that the ejection liquid may not contact with the heater directly, and pressure generated by growing a bubble in the bubble-generation liquid is transmitted to the ejection liquid by deformation of the flexible diaphragm. By such construction, prevention of deposit on the surface of the heater, improvement of freedom in selection of the ejection liquid and so on can be achieved.
However, in the liquid-ejection head having a construction, in which the ejection liquid and the bubble-generation liquid are separated completely as set forth above, since the pressure generated by growing a bubble in the bubble-generation liquid is transmitted to the ejection liquid by expanding and contracting deformation of the flexible diaphragm, the pressure of the bubble generation can be absorbed by the flexible diaphragm in significant extent. Also, magnitude of deformation of the flexible diaphragm is not so large. Therefore, while it is possible to separate the ejection liquid and the bubble-generation liquid by the flexible diaphragm, there are cases where an energy efficiency and an ejection force of the head are lowered.
The present inventors and their coworkers have been made a close study of improving the fundamental ejection characteristics of the head to an extremely high level which are not expected by the man skilled in the art. The results of their study have been disclosed in the previous application. In this document, the study is performed with three different technical analyses: a first one mainly focused on the mechanism of the movable member in the liquid-flowing passage from the view point of the principle of liquid ejection; a second one mainly focused on the mechanism of ejecting a liquid by an effect of bubble generation; and a third one mainly focused on a bubble-forming area on a heater element for the bubble generation. Consequently, it discloses a new-from-the-ground-up configuration of the head where the bubble generation can be positively controlled if a free end of the movable member is positioned on the nozzle side with respect to a supporting end thereof and a surface of the movable member is positioned so as to face the heater element or the bubble-forming area.
For attaining the improvement on the liquid-ejection efficiency and the liquid-ejection speed, the above document discloses that the positive control of the bubble generation can be attained with the consideration of the amount of energy to be supplied from a growing bubble i.e., with the consideration of the downstream components of the growing bubble. The orientation of the downstream components of the growing bubble should be effectively changed in the direction of liquid ejection. Furthermore, a refill rate can be also improved extensively when the configuration of the liquid-supplying passage and the arrangement of the movable element.
When we focus attention on the condition of storing the liquid-ejection head of the prior document, we find that the liquid-flowing passage can be kept from occurring the adhesion of liquid in advance by forcefully replacing a liquid in the liquid-flowing passage with another type of liquid which is difficult to adhere.
From the viewpoint of the information described above, the liquid-ejection head in the type of using a pair of flow passages requires any good scheme to prepare the recording liquid if the image quality of the recording should be improved. In this configuration, one of those flow passages is for a bubble-forming liquid and the other is for a recording liquid.
Thus, the bubble-forming liquid may be of having a composition appropriate to the bubble formation, while the recording liquid may be of having a composition appropriate to the image-recording. The latter may be, for example, a pigment ink (i.e., an ink for improving the properties of waterproof, concentration, quality of characters, and so on) when the user desires the improvements in a recording concentration and a sharpness of image to be printed on a sheet of ordinary paper. In addition, it is possible to perform a favorable ejection without need to worry about foaming and burning of the recording liquid.
In the case of the head in the type of single-layered nozzles as decried above, a solidified ink can be removed by means of the conventional recovering system when an ink in the nozzle is solidified and attached to an inner wall of the nozzle after reserving the head for the long term. In the case of the head in the type of two-layered nozzles, however, there is no effective recovering system for the recording nozzles being arranged as one layer (recording layer), in which a recording liquid can be easily adhered to an inner wall of each nozzle. For example, there is an idea of removing the adhered material by the application of heat if the adhesion of liquid is occurred in the recording nozzles. In this case, however, the applied heat is conducted into another set of the nozzles being arranged under the recording nozzles through a heat-insulating layer. Thus the adhered ink will be hardly dissolved by the application of heat.
The flow resistance of the blocked upper nozzles is much higher than that of the corresponding lower nozzles. If the conventional recovering system is used for introducing flesh liquid into the upper nozzles, the conventional recovering system will draw in fluid from the lower nozzles by suction instead of drawing in the recording liquid from the upper nozzles being blocked with the adhered material as a result of the difference between their flow resistance. Consequently, the adhered material cannot be removed and the flesh ink cannot be introduced into the upper nozzles.
Accordingly, there is the need for solving the problems of difficulty in recovering the ejection characteristics of nozzles in two-layered nozzle structure by using the conventional recovering system or the application of heat when one of the nozzle layers are blocked, and especially difficulty in re-filling fresh ink into the recording nozzles for the recording liquid appropriate to the recording but not to the long term reservation by removing the adhered material using the conventional recovering system.